1. Field of the Invention
The present invention relates to automatic dishwashers and more specifically to a cycle or method of operation for an automatic dishwasher wherein the amount of soil particles or film which remains on a dishload at the conclusion of a dishwasher cycle is minimized.
2. Description of the Related Art
Modern automatic dishwashers are designed to receive a soiled dishload, wash the dishes or dishware items, rinse the dishes and then dry the dishes. Accordingly, prior art dishwashing machines or dishwashers have program cycles which include one or more wash steps, one or more rinse steps and a drying period. The wash step or steps are designed to remove soils from the dishes while the rinse step or steps are designed to flush the soils to drain along with detergents used to remove the soils. Prior to each wash or rinse step there is an initial fill period wherein a charge of water is supplied into the dishwasher. Each wash or rinse step comprises a period of pump operation wherein the wash liquid within the dishwasher is recirculated. In a wash step, detergent is added into the dishwasher along with the fill water. After each wash and rinse step, wash liquid is drained from the dishwasher. For example, a common dishwasher cycle may comprise the following: an initial fill step, a wash step, a drain step, a fill step, a rinse step, a drain step, a fill step, a rinse step and a final drain step followed by a drying period.
The number of wash and rinse steps in a dishwasher program cycle may be varied in accordance with the desired cleaning performance. As can be appreciated by one skilled in the art, dishwashing performance may be improved by having more than one wash step and more than one rinse step. However, to minimize water usage, it is desirable to minimize the number of fills or water changes. Accordingly, in the field of dishwasher design, there is a tension between maximizing wash performance and minimizing the amount of water used for an entire program cycle. There is a need, therefore, for dishwasher designs (including program cycle designs) which minimize water consumption but deliver excellent washing performance.
One recognized problem in achieving excellent wash performance is referred to as filming. Filming occurs when film producing contaminants such as minute water borne detergent and soil particles are left on the dishload after the dry period is completed. Generally, film producing contaminants are particles that are present in the liquid of the final rinse step. At the conclusion of the final rinse step, the rinse liquid remaining on the dishload contain these particles. Once the rinse liquid is evaporated during the drying step, the contaminants are deposited on the dishes in the form of an objectionable film or grit.
One of the goals of a rinse cycle in a dishwasher is to rinse the dishes clean of film producing contaminants. However, this is difficult to accomplish with a single rinse step because of the water borne detergents and soil particles which remain in the dishwasher after the drain step which precedes the rinse step. Film producing contaminants remain in the dishwasher after drain primarily in the carry-over wash liquid found in the dishwasher sump. As is well known, dishwasher pumps can not completely pump-out all wash liquid from a dishwasher during drain. A small amount of wash liquid remains in the dishwasher sump as carry-over wash liquid at the conclusion of a drain step. This carry-over wash liquid is a large source of the film producing contaminates which are found in the final rinse step.
One relatively effective way to reduce the amount of film producing contaminants in the final rinse liquid is to provide a dishwasher program cycle which uses more than one rinse step. Unfortunately, additional rinse steps are undesirable due to the aforementioned desire to minimize water usage.
From the above, it can be understood that there exists in the prior art a need for an improved dishwasher cycle which addresses the problem of filming while at the same time recognizes the need to minimize water usage.